I previously wrote about the role lactic acid can play in disease. This raised the question of whether foods and supplements can buffer metabolic acidity. If so, which foods or supplements are most beneficial? Does pH correlate to the effect on the acid-base balance of the body?
This is important because:
- Chronic acid load can deplete alkalinizing minerals, leading to e.g. calcium bone loss.
- Long Covid may be caused by metabolic acidosis: https://researchaidnetworks.org/hypothesis-summary/
After researching this, I concluded that a food's pH does not directly correlate with its impact on overall acid base balance. Potential Renal Acid Load (PRAL) is determined by mineral and protein composition, not its inherent acidity.
For example:
- Lemons taste acidic due to citric acid, but have a negative PRAL (alkaline-forming) because they're rich in potassium and other compounds that generate bicarbonate when metabolized
- Animal proteins may not taste acidic but have a high positive PRAL (acid-forming) due to sulfur-containing amino acids that get metabolized to sulfuric acid.
The key biochemical factors that determine a food's PRAL include:
- Protein content (especially sulfur amino acids) - metabolized to produce acids
- Mineral content:
- Potassium, calcium, magnesium - metabolized to produce bicarbonate (alkaline)
- Phosphorus, chloride - contribute to acid load
- Organic acid content - intermediates in the citric acid cycle (Krebs cycle), their oxidation generates bicarbonate. Each molecule of malate or citrate metabolized can generate multiple bicarbonate molecules.
Details
The pH of urine is influenced by the body's metabolic acid load and the kidney's ability to regulate hydrogen ion (H⁺) excretion. The kidneys play a crucial role in maintaining acid-base balance by adjusting the amount of hydrogen ions eliminated or retained. When the body experiences a metabolic acid load, the kidneys respond by increasing H⁺ excretion. This lowers urine pH, reflecting the increased acid load on the body. However, positive cations can also stimulate renal acid-base regulation, leading to increased hydrogen ion excretion (and bicarbonate (HCO₃⁻) regeneration). This results in a decrease in urine pH, even as the body experiences a reduced metabolic acid load.
Cations can also activate enzymes that convert metabolic acids to bicarbonate. The more positively charged the cation, the more efficiently it can displace hydrogen ions.
Organic acid conjugation to cations enhances alkalinization. For example, citrate enters the citric acid cycle directly and generates multiple bicarbonate (HCO₃⁻) upon oxidation.
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| Table of Common Supplements and Food Additives; their pH and effect on acid-base balance. |
This data shows how solution pH and PRAL effects don't always correlate. For example, while KCl has a neutral pH in solution, it has a slightly negative PRAL due to the potassium content. However, extreme pH (either acid or base) can correlate with PRAL effect.
Categories of Supplements
- Neutral pH, Alkalizing Effect:
- Potassium citrate
- Calcium lactate
- Potassium gluconate
- These demonstrate the pH vs. physiological effect paradox
- Mineral-Organic Complexes:
- Magnesium citrate and malate show slightly acidic pH but strong alkalizing effects
- Zinc citrate has less alkalizing effect despite similar pH
- Simple Salts:
- KCl shows neutral pH with mild alkalizing effect
- NaCl shows neutral pH and neutral physiological effect
- Strong Acids/Bases:
- HCl, KOH, NaOH show correlation between pH and physiological effect
- These are exceptions to the general trend of pH not predicting physiological impact
Alkalinizing Potential Ranking
The formula for PRAL (mEq/100g) is: PRAL = 0.49 × protein (g) + 0.037 × phosphorus (mg) - 0.021 × potassium (mg) - 0.026 × magnesium (mg) - 0.013 × calcium (mg).
Negative PRAL indicates an alkalizing effect on the body.
Example: mice
Mice diets were compared using Dietary Cation Anion Balance (DCAB), a similar metric to PRAL. DCAB is calculated by adding the weighted amount of acidifying anions and alkalizing cations in the diet.
It has been shown in many species that the dietary cation anion balance (DCAB) influences acid base homeostasis and urine pH. With the DCAB, the resulting urinary pH can be predicted with species-specific equations.
DCAB [mmol/kg DM] = 49.9 · Ca + 82.3 · Mg + 43.5 · Na + 25.6 · K − 59.0 · P − 62.4 · S − 28.2 · Cl; mineral content in g/kg DM. (Negative DCAB indicates an acidifying effect on the body.)
The paper found that a negative DCAB results in metabolic acidosis, and "Fed long-term, this can contribute to the reduction of bone mineral density due to a PTH-mediated increase in renal calcium excretion. Metabolic acidosis also induces renal phosphorus excretion, resulting in hypophosphatemia."
Citation: https://www.mdpi.com/2076-2615/11/3/702
Böswald, L.F.; Matzek, D.; Kienzle, E.; Popper, B. Influence of Strain and Diet on Urinary pH in Laboratory Mice. Animals 2021, 11, 702. https://doi.org/10.3390/ani11030702
Example: human athletes
Alkaline water has demonstrated its effectiveness as an alkalizing agent in the treatment of metabolic acidosis in both animal and human research. Past studies have shown that daily intake of 2.5–4 L of alkaline water for 3~6 weeks has significant impacts on anaerobic performance and acid–base balance in athletes. This study showed that alkaline water co-ingested with glutamine led to decreased stress markers in athletes. Masterjohn hypothesizes that glutamine is converted to glutamate to buffer lactic acid in muscles, and that decreasing PRAL contributes to more available glutamine for other metabolic functions..
Citation: https://www.mdpi.com/2072-6643/16/3/454
Lu, T.-L.; He, C.-S.; Suzuki, K.; Lu, C.-C.; Wang, C.-Y.; Fang, S.-H. Concurrent Ingestion of Alkaline Water and L-Glutamine Enhanced Salivary α-Amylase Activity and Testosterone Concentration in Boxing Athletes. Nutrients 2024, 16, 454. https://doi.org/10.3390/nu16030454
Thanks to Claude Sonnet for back-and-forth conversation, and for creating the table and figure above.
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